1. Field of the Invention
The present invention is directed generally to a light weight alternator, and in particular, a permanent magnet-type alternator including a voltage regulator for regulating the voltage output of the permanent magnet-type alternator.
2. Field of the Related Art
Various alternators use wound stator and rotor assemblies in which an electromagnetic force is produced in and around the rotor windings by admitting current through the rotor windings. In such designs, as the magnetic field produced in the spinning rotor couples with the windings at the stator, current is induced in the stator windings. These alternators, however, require brushes or slip rings to maintain a closed circuit for admitting the current necessary in the rotor during rotation. Because the brushes or slip rings are mechanical connections, they are susceptible to wear and corrosion.
The use of permanent magnet alternators have been found to be advantageous since they do not require that current be supplied to the rotor. In other words, the field inherent to and produced by the magnetic material of the permanent magnet alternators induces current in the stator as the magnet poles move in respect to the stator windings. Because it is not required to supply current to the rotor, slip rings and brushes are not required.
While the use of permanent magnet alternators have proven successful for various applications, the prior art systems have several shortcomings. Generally, because the alternator generates excessive heat, internal fans are provided on the drive end to cool the windings and the rotor. This increases the weight of the alternator, and thus, makes it undesirable for use in an automotive or aerospace capacity where fuel efficiency is needed. Moreover, many systems require the attachment of individual magnets to the outer circumferential surface of the rotor, which may result in the failure of the alternator if by chance one or more magnets becomes detached from the rotor due to the high centrifugal forces that result from the rotation of the rotor at high rpm or faulty adhesion between the magnet and surface. Yet another problem associated with permanent magnet alternators is the difficulty associated with controlling the output voltage generated in the stator windings as will otherwise inherently occur when the alternator is driven at variable rotational velocities. These drawbacks of the prior art are especially problematic in the vehicular environment where low cost, high reliability and light weight are all important to achieving a commercially acceptable design.
In view of the foregoing, it is an object of the present invention to overcome the disadvantages in the related art by providing a permanent magnet alternator for use in an automotive or aerospace capacity that is of a size that allows it to be placed in small areas of an automobile or aircraft engine compartment.
It is another object of the present invention to provide a permanent magnet alternator that is light-weight and highly efficient.
It is a yet another object of the present invention to provide a permanent magnet alternator that has a high cooling capacity.
It is still another object of the invention to provide a permanent magnet alternator that allows the rotation of the rotor at high rpm without resulting in the detachment of magnets from the rotor.
It is yet a further object of the invention to provide a permanent magnet alternator with a voltage regulator that independently regulates and controls the charging current produced by the alternator.
These as well as other objects are achieved in accordance with the invention including a permanent magnet alternator assembly provided with a stationary stator, a rotor mounted for rotation within the stator, a winding circuit for generating a magnetic flux, a plurality of permanent magnets for attachment to the rotor, and a retaining shield positioned between the rotor and stator for reducing the effects of centrifugal motion of the rotor during operation of the alternator.
The stator includes a substantially cylindrical core or body in which a plurality of stator poles project radially inward from the stator body. Each stator pole is composed of a longitudinal shank portion including a base end which is attached to the stator body and a distal end which is flared to facilitate ease during assembly of the winding circuit.
The rotor has a substantially cylindrical body having a laminated structure including a core section preferably comprising a non-ferromagnetic material that is both light-weight and non-corrosive such as aluminum, and an outer circumferential surface preferably comprising a ferromagnetic material such as steel or the like. The permanent magnets are fixedly mounted or attached to the outer circumferential surface of the rotor body in alternating polarity. In order to further reduce the overall weight of the alternator, it is preferred that light-weight, yet high field permanent magnets are used, such as those composed of Neodymium-Iron-Boron (NdFeB).
The retaining shield is positioned between the stator poles and the permanent magnets to reduce the effects of centrifugal motion of the rotor body during operation of the alternator, and the undesirable effects of vibration. The retaining shield is preferably a cylindrical sleeve composed of a non-ferromagnetic material such as stainless steel. The use of the retaining sleeve is advantageous in that it reduces the centrifugal forces and allows rotation of the rotor at high rpm without resulting in the detachment of magnets from the rotor and the possible destruction of the alternator.
In a second embodiment, the permanent magnet alternator assembly includes a laminated, bifurcated rotor having a first rotor section and a second rotor section, each rotor section having a substantially cylindrical body composed of a light-weight, non-ferromagnetic material such as aluminum, and an outer circumferential surface composed of a ferromagnetic material such as steel.
A plurality of fan-like projections are provided equidistant on the peripheral surface of each rotor section. The placement of the fans directly on the surface of each rotor section is advantageous since it obviates the need for drive end fans for cooling the rotors and windings, and thus, further reduces the overall weight of the alternator. The fan-like projections project outward from the side of each rotor section in order to provide the efficient distribution of air inside the alternator housing. In particular, the projections project along a plane that lies substantially parallel relative to the outer circumferential surface. In this way, high ambient temperatures produced inside the alternator during rotation of the rotor are significantly reduced.
A third embodiment of the invention includes a permanent magnet alternator having a stator including a substantially cylindrical body and a plurality of spaced stator poles that project outward from a side surface of the stator body. In particular, the stator poles project along a plane lying substantially parallel relative to an outer circumferential surface of said stator body.
A rotor is also provided including a substantially cylindrical body mounted for rotation relative to the stator body in a face-to-face spatial relationship, as opposed to the conventional manner of rotating inside or outside of the stator. Moreover, a plurality of permanent magnets are fixedly mounted equidistant on the rotor body in alternating polarity and project outward from a side surface of the rotor body. In particular, each permanent magnet projects along a plane lying substantially parallel relative to an outer circumferential surface of the rotor. In this way, the rotor body may be operatively positioned relative to the stator body such that the permanent magnets are rotatably aligned in a face-to-face manner with the stator poles so as to generate a continuous alternating flux density magnetic field along a primary flux path.
The winding of the conductors or winding circuit on the stator poles in accordance with this embodiment is advantageous over conventional winding concepts in that the winding circuit does not require being pulled around and over the outer circumferential surface of the stator. This results in a less bulky design radially, which is further advantageous in terms of weight.
Moreover, a voltage regulator circuit is also provided for regulating the charging current produced by the permanent magnet alternators described above. The regulator circuit is adapted to receive the output of a 3-phase permanent magnet alternator, however, other single phase or multi-phase permanent magnetic alternators could be used to provide the input to the regulator circuit.
The voltage regulator circuit in accordance with this embodiment of the invention includes a rectifier circuit having an output and an input adapted to be connected to a stator mounted coil for converting alternating potential to a time varying single potential on said output, a current control circuit connected between the output of the rectifier circuit and the load and for cycling between (1) a conductive state to conductively connect said rectifier circuit with the load, and (2) a non-conductive state to isolate the rectifier circuit from the load. Also provided is an instantaneous voltage sensing circuit connected with the output of the rectifier circuit and the current control circuit for measuring the instantaneous voltage appearing on the output and for causing the current control circuit to assume its conductive state when the instantaneous voltage is above a predetermined amount.
Last, a regulator control circuit is provided for (1) sensing the voltage applied to the load by the current control circuit and for causing the current control circuit to assume its non conductive state when the voltage applied to the load is above a desired level, and (2) for shortening the time during which the current control circuit is in its conductive state as the voltage applied to the load approaches the predetermined level. The regulator control circuit may include a sensing circuit for determining if a short circuit exists by measuring the period of time the current control circuit is in a conductive state. The regulator control circuit may further include an input connected with an RC circuit for adjusting the operating voltage of the regulator circuit in response to changes in the duty cycle of the current control circuit.
The voltage regulator circuit may include an alternator failure indicator responsive to an over voltage or under voltage condition to produce an alternator failure indication. The voltage regulator circuit may further include a load dump circuit selectively connectable in parallel with the load, the load dump circuit being connected in parallel when the voltage applied to the load continues to increase for more than a predetermined period.